nested array index python-CodePudding

scores = [[0,0]]*10
scores[1][1]  = 1
print(scores)
>>[[0, 1], [0, 1], [0, 1], [0, 1], [0, 1], [0, 1], [0, 1], [0, 1], [0, 1], [0, 1]]

I want to increment at a specific position in a nested list in python, but am incrementing the entire list instead. Can anyone explain this behavior?

CodePudding user response：

This is because python is first creating the list, then is creating the reference ten times. In other words, using this method only one list is created. Try this:

scores = []
for i in range(10):
    scores.append([0, 0])
scores[1][1]  = 1
print(scores)

Output:

[[0, 0], [0, 1], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]

CodePudding user response：

scores = [[0,0]]*10 makes 10 copy of the same objects. If you examine the id() of the list's elements, for example by id(scores[3]), you can see their references are the same. If you want to have different objects in your list, you should use something like: scores = [[0,0] for i in range(10)]